1. Field of the Invention
The present invention relates generally to propulsion systems for marine vessels, and more particularly to an outboard marine propulsion system with a closed loop lower unit heat exchanger and the various components thereof.
2. Description of the Related Art
Outboard motors that are manufactured today use an open loop cooling system where water is drawn from the marine operating environment into the outboard motor for cooling purposes. The water is passed through the engine, oil cooler, fuel cooling system, and exhaust and then returned to the marine operating environment. Such an open loop cooling system is both efficient and cost effective, but there are some drawbacks to an open loop cooling system that can result in not only performance issues, but early engine failure.
An open loop cooling system can lead to the plugging of internal engine passages through debris such as mud, stones, weeds, leaves, and the like, all of which can be drawn in with the intake water used for cooling. In addition, when an outboard motor with such an open loop cooling system is operated in salt water, the untreated cast aluminum cooling channels inside the outboard motor will oxidize over time. Small water channels within the outboard motor will become plugged with aluminum oxide that breaks free from oxidized areas within the engine, plugging those cooling channels and causing the engine to run hot or overheat and eventually fail. While aluminum is less corrosive than steel and iron products, it will still oxidize and eventually fail over time. Plugged water channels may cause an engine to overheat with resulting damage. In some cases, the oxidation may be so severe that the internal walls of the motor become porous such that cooling water enters the combustion side of the engine, causing engine failure and the need for engine replacement, a costly proposition.
While outboard motor manufacturers use a plastic intake screen to prevent large solids from being drawn into the engine through the open loop cooling system, overheating will occur when the plastic screen is covered with debris such as weeds, leaves, and the like. Once the intake screen is covered with debris, water flow to the engine stops, leading to engine overheating and at a minimum the destruction of the water pump impeller within the engine.
What is needed is a closed loop cooling system for an outboard motor. What is further needed is a closed loop cooling system for an outboard motor that allows a traditional marine outboard motor to be converted into a closed loop cooling system.
It is thus an object of the present invention to provide such a closed loop cooling system and also provide for such a marine propulsion unit, as will be further described herein. These and other objects of the present invention are not to be considered comprehensive or exhaustive, but rather, exemplary of objects that may be ascertained after reading this specification and claims with the accompanying drawings.